Index: lib/Target/Mips/AsmParser/MipsAsmParser.cpp
===================================================================
--- lib/Target/Mips/AsmParser/MipsAsmParser.cpp
+++ lib/Target/Mips/AsmParser/MipsAsmParser.cpp
@@ -176,6 +176,12 @@
 
   bool hasMips4() const { return STI.getFeatureBits() & Mips::FeatureMips4; }
   bool hasMips32() const { return STI.getFeatureBits() & Mips::FeatureMips32; }
+  bool hasMips32r6() const {
+    return STI.getFeatureBits() & Mips::FeatureMips32r6;
+  }
+  bool hasMips64r6() const {
+    return STI.getFeatureBits() & Mips::FeatureMips64r6;
+  }
 
   bool parseRegister(unsigned &RegNum);
 
@@ -905,6 +911,14 @@
     }
   }
 
+  // SSNOP is deprecated on MIPS32r6/MIPS64r6
+  // We still accept it but it is a normal nop.
+  if (hasMips32r6() && Inst.getOpcode() == Mips::SSNOP) {
+    std::string ISA = hasMips64r6() ? "MIPS64r6" : "MIPS32r6";
+    Warning(IDLoc, "ssnop is deprecated for " + ISA + " and is equivalent to a "
+                                                      "nop instruction");
+  }
+
   if (MCID.hasDelaySlot() && Options.isReorder()) {
     // If this instruction has a delay slot and .set reorder is active,
     // emit a NOP after it.
Index: lib/Target/Mips/Mips32r6InstrInfo.td
===================================================================
--- lib/Target/Mips/Mips32r6InstrInfo.td
+++ lib/Target/Mips/Mips32r6InstrInfo.td
@@ -14,7 +14,6 @@
 include "Mips32r6InstrFormats.td"
 
 // Notes about removals/changes from MIPS32r6:
-// Unclear: ssnop
 // Reencoded: jr -> jalr
 // Reencoded: jr.hb -> jalr.hb
 // Reencoded: sdbbp
Index: test/MC/Mips/mips32r6/valid.s
===================================================================
--- test/MC/Mips/mips32r6/valid.s
+++ test/MC/Mips/mips32r6/valid.s
@@ -10,7 +10,8 @@
 #   rs > rt
 # appropriately for each branch instruction
 #
-# RUN: llvm-mc %s -triple=mips-unknown-linux -show-encoding -mcpu=mips32r6 | FileCheck %s
+# RUN: llvm-mc %s -triple=mips-unknown-linux -show-encoding -mcpu=mips32r6 2> %t0 | FileCheck %s
+# RUN: FileCheck %s -check-prefix=WARNING < %t0
 
         .set noat
         # FIXME: Add the instructions carried forward from older ISA's
@@ -138,3 +139,5 @@
         sc      $15,-40($s3)     # CHECK: sc $15, -40($19)       # encoding: [0x7e,0x6f,0xec,0x26]
         clo     $11,$a1          # CHECK: clo $11, $5            # encoding: [0x00,0xa0,0x58,0x51]
         clz     $sp,$gp          # CHECK: clz $sp, $gp           # encoding: [0x03,0x80,0xe8,0x50]
+        ssnop                    # WARNING: [[@LINE]]:9: warning: ssnop is deprecated for MIPS32r6 and is equivalent to a nop instruction
+        ssnop                    # CHECK: ssnop                  # encoding: [0x00,0x00,0x00,0x40]
Index: test/MC/Mips/mips64r6/valid.s
===================================================================
--- test/MC/Mips/mips64r6/valid.s
+++ test/MC/Mips/mips64r6/valid.s
@@ -10,7 +10,8 @@
 #   rs > rt
 # appropriately for each branch instruction
 #
-# RUN: llvm-mc %s -triple=mips-unknown-linux -show-encoding -mcpu=mips64r6 | FileCheck %s
+# RUN: llvm-mc %s -triple=mips-unknown-linux -show-encoding -mcpu=mips64r6 2> %t0 | FileCheck %s
+# RUN: FileCheck %s -check-prefix=WARNING < %t0
 
         .set noat
         # FIXME: Add the instructions carried forward from older ISA's
@@ -156,3 +157,5 @@
         clz     $sp,$gp          # CHECK: clz $sp, $gp           # encoding: [0x03,0x80,0xe8,0x50]
         dclo    $s2,$a2          # CHECK: dclo $18, $6           # encoding: [0x00,0xc0,0x90,0x53]
         dclz    $s0,$25          # CHECK: dclz $16, $25          # encoding: [0x03,0x20,0x80,0x52]
+        ssnop                    # WARNING: [[@LINE]]:9: warning: ssnop is deprecated for MIPS64r6 and is equivalent to a nop instruction
+        ssnop                    # CHECK: ssnop                  # encoding: [0x00,0x00,0x00,0x40]